How to add Content Security Policy to Firefox extension

Question

I have a plugin which I have to support both on Chrome and Firefox browsers. The plugin does cross script loading.

In Chrome, by adding the content security policy i

Answer 1

There are plans in the future to add content policy natively in the SDK (bug 852297), but there is a 3rd party module that should get you close to where you want to be: policy.js

Answer 2

I couldn't find a simple solution for my problem and upon looking up some firefox plugin extensions i had to come up with my own solution as below. The below solution was tested on FF 24.0 but should work on other versions as well.

Cc["@mozilla.org/observer-service;1"].getService(Ci.nsIObserverService)
    .addObserver(_httpExamineCallback, "http-on-examine-response", false);

function _httpExamineCallback(aSubject, aTopic, aData) {
    var httpChannel = aSubject.QueryInterface(Ci.nsIHttpChannel);

    if (httpChannel.responseStatus !== 200) {
        return;
    }

    var cspRules;
    var mycsp;
    // thre is no clean way to check the presence of csp header. an exception
    // will be thrown if it is not there.
    // https://developer.mozilla.org/en-US/docs/XPCOM_Interface_Reference/nsIHttpChannel
    try {    
        cspRules = httpChannel.getResponseHeader("Content-Security-Policy");
        mycsp = _getCspAppendingMyHostDirective(cspRules);
        httpChannel.setResponseHeader('Content-Security-Policy', mycsp, false);
    } catch (e) {
        try {
            // Fallback mechanism support             
            cspRules = httpChannel.getResponseHeader("X-Content-Security-Policy");
            mycsp = _getCspAppendingMyHostDirective(cspRules);    
            httpChannel.setResponseHeader('X-Content-Security-Policy', mycsp, false);            
        } catch (e) {
            // no csp headers defined
            return;
        }
    }

};

/**
 * @var cspRules : content security policy 
 * For my requirement i have to append rule just to 'script-src' directive. But you can
 * modify this function to your need.
 *
 */
function _getCspAppendingMyHostDirective(cspRules) {
  var rules = cspRules.split(';'),
    scriptSrcDefined = false,
    defaultSrcIndex = -1;

  for (var ii = 0; ii < rules.length; ii++) {
    if ( rules[ii].toLowerCase().indexOf('script-src') != -1 ) {
        rules[ii] = rules[ii] + ' <My CSP Rule gets appended here>';
        scriptSrcDefined = true;
    }

    if (rules[ii].toLowerCase().indexOf('default-src') != -1) {
        defaultSrcIndex = ii;
    }
}

  // few publishers will put every thing in the default (default-src) directive,
  // without defining script-src. We need to modify those as well.
  if ((!scriptSrcDefined) && (defaultSrcIndex != -1)) {
    rules[defaultSrcIndex] = rules[defaultSrcIndex] + ' <My CSP rule gets appended here>';
  }

  return rules.join(';');
};